Fuel cells are used to convert chemical energy of a fuel directly to electricity without going through combustion and the loss of efficiency due to the Carnot cycle limitation. Since there is no combustion in fuel cells, environmental benefits are obvious. Fuel cells can also be used in the deployment of renewal energy devices, such as wind or solar electricity generators, for storing the energy as fuel generated and transmitting the energy to a different location and at a different time.
There are various types of fuel cells. A common type of fuel cells is hydrogen-oxygen fuel cells, in which hydrogen is used as fuel and is combined with oxygen to form water. Methanol fuel cells have also been used in various power devices. For example, direct methanol fuel cells can be used to replace existing batteries in portable electronic products, such as notebook computers and mobile phones.
Typically, direct methanol fuel cells use a polymer electrolyte membrane between anode and cathode to separate the anode and cathode contents, preventing internal electronic current between the two electrodes and providing ionic conductivity within the fuel cell. For example, Nafion®, a perfluorosulfonic polymer, is a commonly used proton electrolyte membrane for fuel cells. This type of fuel cells is referred to as polymer electrolyte membrane (PEM) fuel cells. They can be used in operations under room temperature to moderate temperature (below about 180° C.).
Various attempts have been made to develop a polymer electrolyte membrane having a low methanol permeability, such as by synthesizing a new type of polymer to replace Nafion, or by modifying Nafion to form a composite membrane. However, such attempts can either undesirably affect proton conductivity, incur additional costs, or cause instability, hindering their practical applications in direct methanol fuel cells.
The present invention provides a composite membrane with a low methanol permeability and high proton conductivity. In particular, the present invention provides a nanocomposite membrane capable of improving the performance of direct methanol fuel cells. The present invention also relates to a method for making a composite membrane having low methanol permeability and high proton conductivity.